Five years ago NASA’s Terra satellite began measuring Earth’s vital signs with a combination of
accuracy, precision, and resolution the world had never before seen. Today, Terra completes the fifth year in
what was scheduled to be at least a 6-year mission to advance understanding of Earth’s climate system,
and to help improve our quality of life.

Launched on December 18, 1999, Terra’s five onboard instruments began science operations in February 2000.
Terra’s goal is to assess the health of the planet by providing comprehensive information about Earth’s
land, oceans and atmosphere. From its vantage point 438 miles above our world, Terra orbits the Earth more than
fourteen times a day and observes nearly the entire globe.

Sending home roughly 1 million megabytes of data per day, Terra is helping scientists all over the world tackle
important questions about the causes and effects of environmental changes. While the mission is still in the
process of fulfilling its main science objectives, Terra’s portfolio of achievements to date already marks
the mission a resounding success.

A key focus of the Terra mission is to help scientists measure the movements of carbon through Earth’s
climate system. To meet their needs for industry, agriculture, and transportation, humans annually release more
than 7 billion tons of carbon into the atmosphere through the burning of fossil fuel. Yet, scientists cannot
account for where all this carbon ends up. Between 1 and 2 billion metric tons of carbon per year are
“missing” from the global carbon budget.

Today Terra is providing scientists with some important clues to help them solve the mystery of the missing
carbon. For example, every eight days the mission’s Moderate Resolution Imaging Spectroradiometer (MODIS)
instrument produces a global map of where and how much carbon dioxide is drawn out of the air and fixed by
vegetation during photosynthesis.

“These maps give scientists the best global measure ever made of the amount of carbon taken up by plants,”
said Jon Ranson, Terra Project Scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md.
“Carbon fixation by plants is the basis for capturing and storing the energy that fuels our world’s
living systems and forms the foundation of the food web.”

This false-color map represents the Earth’s carbon “metabolism” — the rate at which plants
absorbed carbon out of the atmosphere. The map shows the global, annual average of the net productivity of
vegetation on land and in the ocean during 2002. The yellow and red areas show the highest rates, ranging from 2
to 3 kilograms of carbon taken in per square meter per year. The green, blue, and purple shades show progressively
lower productivity. (NASA image courtesy Reto Stockli, Earth Observatory)
More information.

Tracking plant growth is also an important way in which Terra gives back to society. Scientists and resource
managers are using Terra’s Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and MODIS
instruments to monitor large agricultural regions and assess the health of croplands. These instruments produce
maps of the “greenness” of the landscape, which scientists use as a measure of how much plant growth
is occurring.

The Terra ASTER instrument acquired these images over the U.S. Department of Agriculture’s Grazing Lands
Research Laboratory near El Reno, Oklahoma, on Sept. 4, 2000. In the top image, bright red colors indicate green
vegetation, which at this time of year only includes irrigated lands and riparian zones. Gray-green colors represent
harvested winter wheat fields. Dendritic drainage patterns are clearly depicted in the lower left and upper right
portions of the scene. ASTER’s three visible and near-infrared bands were used to make this image. The second
panel shows the abundance of green vegetation (referred to as Normalized Difference Vegetation Index, or NDVI).
NDVI is a measure of vegetation density and health. In this image, blue represents dense vegetation cover and
yellow and red shows progressively less dense vegetation. (NASA images courtesy Andrew French, ASTER Science Team)
More information.

Moreover, by comparing today’s Terra vegetation greenness maps to long-term averages, scientists can gauge
when plants are under stress due to extreme heat or drought. The U.S. Department of Agriculture’s Foreign
Agricultural Service uses Terra data to produce maps of drought across major food production regions in developing
countries. In terms of lives lost and economic impact worldwide, drought is the costliest of natural disasters.
Terra data are helping resource managers improve foreign market access for U.S. agricultural products,
particularly during times of need.

Drought has been looming over Kenya for several years, leaving many regions of the country parched and hungry. Now,
as the 2004/2005 harvest draws to a close, the cereal deficit has grown to 300,000 metric tons, which means that up
to 2.7 million people will need food aid this season-an unusually high number for Kenya. This map shows Normalized
Difference Vegetation Index (NDVI) anomaly, recorded by the Terra MODIS instrument on February 3, 2005. The brown
clusters in the Coast and Eastern provinces show patterns of dryness where vegetation is less dense than it has been
in the past. More pronounced drought areas surround Central Province. Grey pixels indicate regions where data were
not available. An arch of green through the center of the country reveals where there has been plentiful rainfall
and the vegetation is thriving. (NASA image courtesy Jesse Allen, Earth Observatory)
More information.

Benefits to Society

Many of Terra’s achievements benefit society. For example, Terra data have helped improve scientists’ ability to
predict the weather. Terra’s ability to track the speed, direction, and height of clouds allows scientists to accurately
measure how hard and which way the wind is blowing over areas where they had precious little data before. Terra’s
Multi-angle Imaging Spectroradiometer (MISR) measures of wind heights over the Pacific Ocean have proven more accurate than our
best operational weather satellites. (Please read Tracking Clouds
for more details.)

Two years ago meteorologists at the European Centre for Medium-Range Weather Forecasts (ECMWF) began using Terra
MODIS data to track clouds over the Arctic Circle. Before Terra, scientists had to make mostly educated guesses
about wind strength and direction. But given Terra’s updates every 99 minutes over the Arctic, scientists
are able to feed their computers with much more timely and accurate information. The result is a 3-hour advance
in the accuracy of their forecasts. This advance may not seem like much but one expert equates that to a whole
year’s worth of research and development by the ECMWF. (Please read
Polar Wind Data Blow New Life into Forecasts for more details.)

Terra has helped weather forecasters in other ways too. Before Terra, scientists made assumptions about how much
sunlight gets reflected by the surface in seldom-measured parts of the world, such as the Sahara Desert. Today
Terra provides scientists with much more accurate information on Earth’s albedo (or reflected sunlight) over
areas where before they could only make educated guesses. The end result is improved weather forecasts in Northern
Africa, the Arabian Peninsula, and across great expanses of the mostly uninhabited boreal forests of North America
and Asia. (Please read Measuring
Earthshine: How New Terra Data are Improving Weather and Climate Forecast Models for more details.)

A classical intense hurricane is shown in this view of Juliette, captured by the Terra MISR instrument on
September 26, 2001. On the left is a true-color image produced by MISR’s nadir (vertical-viewing) camera.
Impressive spiral arms wrapped around the eye are apparent. Several areas of convective clouds can be discerned
along the arms. On the right is the cloud-top height field derived using automated computer processing of the
data from multiple MISR cameras. Relative height variations are well represented, such as the clearing within the
storm’s eye. (NASA image courtesy Image courtesy NASA/GSFC/LaRC/JPL, MISR Team.)
More information.

Another of Terra’s benefits to society has been the development of natural hazard warning systems. A mission goal is to
help humans avoid emerging hazards where possible, to reduce the impact of hazards where avoidance is not possible, and to more
accurately assess the damage where and when natural disasters happen.

The mission’s unique combination of sensors allows scientists worldwide to monitor fires, floods, severe storms, and
volcanic activity in near real time. Today organizations all over the world use data from four different instruments aboard
Terra as part of their ongoing efforts to monitor the causes and effects of natural hazards.

Moreover, more than 80 receiving stations positioned around the world routinely and freely receive Terra data as it is
broadcast live and continuously. These receiving stations push Terra data to more than 800 operational users for a wide
range of research and practical science applications.

“Timely data from the Terra satellite are being used to produce maps of where active fires are burning all over
the world,” said Ranson. Used operationally by USDA Forest Service and the U.S. National Interagency Fire Center,
Terra MODIS and ASTER data help firefighters develop strategies for fighting the fires as well as assessing the severity
of the burns. (Please read From Space to the Outback and
Satellites Aid Burned Area Rehabilitation for more details.)

“This same technology also allows scientists to map the locations of volcanic hot spots all over the world,”
continued Ranson. “Such information has great potential to save lives, not just for people living near active volcanoes,
but also for commercial airlines that routinely fly near them.”

The new MODIS albedo data product reveals in striking detail how widely varied the terrain is across Northern Africa
and the Arabian Peninsula. The variation across the land’s surface affects how much solar radiation is absorbed and
how much is reflected back up into the overlying atmosphere. This new data product should significantly improve
weather forecast models for that region. This image was produced using data composited over a 16-day period, from
April 7-22, 2002. (Image courtesy Elena Tsvetsinskaya, Boston University)
More information.

How Terra Tracks Pollution

Wildfires and volcanoes aren’t just hazards on the ground. They produce plumes of smoke and gas that can
travel hundreds or even thousands of miles downwind, affecting the chemistry of the atmosphere and impacting the
quality of the air we breathe. Terra carries three instruments designed to observe and measure these plumes.

Terra’s Measurements Of Pollution In The Troposphere (MOPITT) instrument provides the first global maps of
the concentration of carbon monoxide in Earth’s lower atmosphere. This gaseous pollutant results from fires
and human burning of fossil fuel. It is important to monitor carbon monoxide because it is a precursor to the
formation of poisonous ozone in the lower atmosphere, and because it shows one way in which humans affect the air
we breathe.

Thus, Terra’s measurement capabilities allow scientists to distinguish between natural changes in
Earth’s environment and changes caused by humans. As such, the mission can help warn of cases when we become
hazardous to ourselves. (Please read NASA’s
Terra Satellite Tracks Global Pollution for more details.)

The U.S. Environmental Protection Agency (EPA) picked up on this fact and began integrating Terra data into its
ongoing efforts to monitor and regulate air quality. EPA scientists found that Terra’s combined precision and
big picture perspective far exceed their ability to measure aerosol and carbon monoxide pollution from individual
locations all across the United States. Now, whenever thick smoke plumes billow from wildfires in western states
all the way to Maine, or whenever industrial smog drifts out of the Midwest and over the Eastern Seaboard, EPA
scientists use Terra data to trace the pollution back to its source as well as predict its future pathways. (Please
read A New IDEA in Air Quality Monitoring for more details.)

Colorless, odorless, and poisonous, carbon monoxide (CO) is one of the six major air pollutants regulated in the United States
(and by other nations around the world, as well). CO is created when carbon-based fuels, like fossil fuels or wood, don’t burn
completely or efficiently. The image above shows the average amounts and geographic sources of CO from April, May and June for
the years 2000 through 2004. Blue areas have little or no atmospheric CO, while progressively higher levels are show in green,
yellow, orange, and red. (Images courtesy Cathy Clerbaux, NCAR Atmospheric Chemistry Division)
More information.

What do all these changes in Earth’s environment and climate system say about the health of our home planet?
Terra is designed to help scientists answer this question. But, scientists caution, this question is complex and
multi-faceted so the answer will not come overnight.

EPA and NASA scientists fuse ground-based measurements with satellite data, meteorological measurements, and computer models
to get a big-picture view of air pollution. This data fusion produces a map with several layers of information. The background
is satellite data from MODIS, with aerosol optical depth in color (aerosol concentrations increasing from blue to red) and cloud
thickness in shades of gray (thickness increasing from gray to white). Wind speed and direction are shown with white arrows, and
ground-based measurements of air quality appear as colored dots (air pollution increasing from green to red). Fire locations from
the GOES-12 satellite are marked with pink or violet diamonds. The image shows conditions on July 19, 2004. The large area of
dense aerosols across the Midwest was caused by widespread fires in Alaska and Canada (see animation).
(Map courtesy NASA/EPA/NOAA/CIMSS IDEA program)

Balancing Earth’s Energy Balance

Unlike weather forecasting and natural hazard monitoring, which rely upon near-real-time regional observations made
on time scales from minutes to days, assessing the health of Earth’s entire climate system relies upon
collection of data over the entire globe on time scales from years to decades. Will Earth continue its present
warming trend and, if so, how rapidly will it warm?

Because the Sun powers our world’s climate system, to answer that question scientists must determine whether
Earth’s energy budget is in balance. That is, over the course of a year, does the amount of solar energy
entering the climate system equal the total amount of energy that is escaping back into space?

“Generally, the answer is yes, Earth’s energy budget is in balance and the climate system is
stable,” explained Bruce Wielicki, Senior Scientist for Earth Science at NASA’s Langley Research Center,
Hampton, Va. “But over the last 150 years, as humans have introduced increasing amounts of greenhouse gases
and aerosol particles into the atmosphere, we have changed how our world reflects and absorbs solar energy as well
as how it emits thermal energy (or heat).”

According to Wielicki, some of these changes result in more sunlight reflected back into space, thereby cooling
the planet. On the other hand, some of the changes result in more solar energy getting trapped within Earth’s
climate system, thereby warming the planet. Which changes will predominate in the future and how rapidly will the
changes occur?

“We don’t know,” said Wielicki. “To answer that question we have to track a long list of
variables all over the Earth over a long period of time.”

Then we have to spend time and brainpower analyzing all those data. Among the “variables” Terra tracks
are cloud and aerosol concentrations in the sky, snow and ice cover on the surface, areas of expanding deserts and
cities, and areas of human deforestation. Each of these variables plays a part in determining how much total energy
gets absorbed into the climate system and how much gets reflected and emitted back to space.

To make matters more complicated, as each of these climate variables change they cause other variables to change.
In one case study, scientists set out to determine how smoke from biomass burning across the Amazon region in South
America affect clouds. Their hypothesis was that the sooty aerosol would modify the clouds by making them brighter
white and longer lasting, thereby enhancing their ability to reflect sunlight and to cool the surface. Instead,
much to their surprise, satellite data revealed that the smoke effectively chokes or limits cloud formation. Thus,
more sunlight gets absorbed into the system and the net result is a regional warming, rather than the enhanced
cooling scientists had expected. (Please read Clouds
Are Cooler Than Smoke for more details.)

All working in concert, and together with the fifteen other NASA Earth Observing System (EOS) satellites
currently in orbit, Terra data are helping scientists untangle the myriad cause-and-effect relationships at work
within Earth’s climate system. And when scientists get to the bottom line on Earth’s radiant energy budget,
Terra’s Clouds and Earth’s Radiant Energy System (CERES) instrument will help ensure they get it
right.

At better than twice the accuracy of its predecessors, CERES makes daily global maps of how much sunlight and
how much heat energy are escaping through the top of the atmosphere. Comparing CERES’ daily global maps of
radiant energy flux with Terra’s other maps of changing variables allows scientists to more precisely
measure the role each variable plays in how the whole system works.

“Terra is Earth science’s first great observatory,” said Wielicki. “It has provided the
most comprehensive and the most accurate global view of the Earth’s climate yet on record. And it has
pioneered the first comprehensive, multi-instrument approach to climate change research.”

It is important to note that Terra is not going it alone. The mission is part of an extended family that includes
sixteen NASA Earth Observing System (EOS) satellites currently in operation.

A portion of the sunlight that reaches Earth is absorbed into the system, while some of the light is reflected by our planet
back into space. Some of the sunlight that gets absorbed is converted to heat and later emitted by the surface and atmosphere
back up into space. This image shows Earth’s net radiation in June 2004. The term “net radiation” refers to
the total amount of sunlight and heat energy that does not escape from the top of the Earth's atmosphere back into space.
Regions of positive net radiation indicate areas of energy surplus in the Earth system (i.e., green regions over the tropics)
and areas of negative net radiation signify regions of energy deficit (such as blue regions over high latitudes and the poles).
(NASA image courtesy Reto Stockli, Earth Observatory)

Together, these EOS missions extend the legacy of global observations begun in the late 1970s by NASA’s
Nimbus satellite and the series of increasingly advanced Earth-observing satellites launched through the 80s and
90s. And yet the data being collected today by Terra and its sister satellites show how NASA has made significant
progress in measurement accuracy.

“The value of a climate record is directly proportional to the length of the record and to its
accuracy,” said Wielicki. “There are no substitutes for these two data qualities.”

Ranson agreed, stating that Terra’s instruments brought new channels that provide data at better
resolutions of time and space than previous satellites. Terra’s instruments are also better calibrated
and collect data from multiple viewing angles, both of which result in data of sufficient quality for studies
of the global climate system.

Since February 2000, Terra’s five instruments have been comprehensively observing and measuring our planet’s
climate system. A goal of the mission is to help scientists distinguish between natural changes and those changes that humans
cause, and to help scientists construct better computer models of how the climate system works. (NASA
animation courtesy Reto Stockli, Earth Observatory)